1. Field of the Invention
This invention relates to a new process for preparing ethyl and n-propyl esters of carboxylic acids. More particularly, the invention relates to a new process for preparing ethyl esters of carboxylic acids from the acids, methanol and syngas using a novel catalyst system.
Specifically, the invention provides a new and improved process for preparing ethyl and n-propyl esters of carboxylic acids, such as ethyl propionate, and n-propyl propinate in good yield from aliphatic carboxylic acids, such as propionic acid, carbon monoxide, hydrogen and methanol, which process comprises contacting a mixture of the carboxylic acid, carbon monoxide, hydrogen and methanol with a catalyst composition comprising a ruthenium-containing compound, a cobalt-containing compound and a quaternary onium salt or base, and heating the resulting mixture at an elevated temperature and pressure for sufficient time to produce the desired ethyl and propyl esters, and then recovering the same from the reaction mixture.
2. Prior Art
Ethyl and n-propyl esters, such as ethyl propionate and n-propyl propionate, are chemicals which have found wide use in industry. They may be used, for example, in the production of anhydrides and in the production of the valuable building blocks, ethylene and propylene. These esters may also be used as solvents and diluents and as softeners for resins.
Various methods have been used in the past for the production of the ethyl esters. The esters can be produced, for example, by reaction of the ethanol with the desired carboxylic acid, both components commonly being obtained from petroleum and agrichemical feedstocks. A direct synthesis of the ethyl esters from syngas would be potentially more economical and highly desirable.
It has been proposed to prepare the ethyl esters of carboxylic acids by carbonylation techniques, but these methods up to the present have not been entirely satisfactory as they give low yields of the desired ethyl esters or use expensive catalysts or catalysts that are difficult to utilize on a large scale. For example, U.S. Pat. No. 4,270,015 and references cited therein disclose various catalyst systems for use in producing ethyl esters by carbonylation. U.S. Pat. No. 4,270,015 discloses the preparation of ethyl esters from syngas using a ruthenium-Group VA ligand catalyst as catalyst. While this process produces the ethyl esters, there is a great deal to be desired as to the selectivity and yield of the desired product.
It is an object of the invention, therefore, to provide a new and improved process for preparing the ethyl and n-propyl esters of carboxylic acids. It is a further object to provide a process for preparing esters, such as ethyl propionate and propyl propionate, from syngas, methanol and a carboxylic acid, such as propionic acid, using a new and improved catalyst system. It is a further object to provide a new process for preparing ethyl and n-propyl esters of carboxylic acids which give improved selectivity and yield. It is a further object to provide a new process for making ethyl and n-propyl esters from syngas using a catalyst system which is suitable for use on large scale operations. These and other objects of the invention will be apparent from the following detailed description thereof.